1. Field of the Invention
The present invention relates generally to a bubble separating apparatus for removing bubbles contained in a liquid, such as lubricants, surface active agents, polymer containing liquid, coating and so forth. More specifically, the invention relates to a bubble separating apparatus which can effectively remove even fine bubbles by a vortical flow created with utilizing flow of the liquid per se.
2. Description of the Related Art
Fine bubbles dispersed in a liquid are known to influence natural properties or performance of the liquid or to be a factor promoting oxidation of the liquid.
For example, engine oils, turbine oils, hydraulic oils and so forth, may contain a large amount of fine bubbles generated due to agitation, circulation, abrupt pressure variation and the like. The amount of fine bubbles increases with the higher speeds and higher outputs according to progress of technologies of engines, turbines, and hydraulic equipment. A large amount of fine bubbles contained in the lubricants tend to cause vibration or abnormal noise in a supply pump, wearing of the vibrating portion, lowering of working pressure and/or working efficiency due to a drop in hydraulic pressure and so forth. Furthermore, increased contact area between the liquid and the fine bubbles promotes degradation of the liquid due to oxidation.
In case of the coating, the fine bubbles contained in the coating may adhere on the surface where a coating layer is to be formed, preventing the coating from being applied thereto and causing irregularity or other defect in the coating layer.
Therefore, it has been required to effectively remove bubbles from liquid.
As a typical bubble separating apparatus, there has been an apparatus which utilizes a flow of the liquid pressurized by a pump to generate a vortical flow of the liquid to concentrate bubbles at the center portion of the vortical flow due to centrifugal force, whereby efficiently and certainly to remove bubbles from the liquid. Commonly owned Japanese Unexamined Patent Publication (Kokai) No. 3-123605 discloses such bubble separating apparatus. The construction of the prior proposed bubble separating apparatus disclosed in the above-identified publication will be discussed briefly with reference to FIG. 1.
In FIG. 1, a vortical flow chamber 2 is defined by a parabola-shaped container 1 having opposite closed ends. In the shown example, the parabola-shaped container 1 is arranged vertically with the larger diameter end. The larger diameter end of the container 1 is surrounded by an annular pipe 3 which is formed integrally with the container 1. A liquid supply inlet 4 is connected to the annular pipe 3. A plurality of openings 5 are formed through the peripheral wall of the upper larger diameter end of the container 1 at intervals for establishing communication between the annular pipe 3 and the vortical flow chamber 2 defined in the container 1. The liquid is supplied from the liquid supply inlet 4 into the annular pipe 3 to circulate therealong and flows into the chamber 2 through the openings 5 to generate vortical flow therein.
The container 1 has a plurality of small holes 6 formed through the peripheral wall in substantially a lower half of the container. The container 1 is disposed in an outer vessel 8 so that the liquid discharged through the holes 6 is received within the outer vessel 8. The outer vessel 8 is formed integrally with the container 1 and the annular pipe 3. The liquid received in the outer vessel 8 is discharged through a liquid discharge outlet 7.
On the other hand, along the center axis of the vortical flow chamber 2 in the container 1, a center conduit pipe 9 is disposed. The center conduit pipe 9 is formed with a plurality of orifices 10 for communicating with the chamber 2. The lower end of the center conduit pipe 9 extends from the lower end of the container 1 and the bottom of the outer vessel 8. The center conduit pipe 9 is adapted to capture bubbles concentrated toward the center portion by centrifugal force exerted due to vortical flow of the liquid within the chamber 2. The bubble containing liquid flowing into the center conduit pipe 9 through the orifices 10 is fed to a bubble discharge outlet 11.
The openings 5 connecting the interior space of the annular pipe 3 and the chamber 2 are formed into such a configuration as to lead the liquid into the chamber 2 along a tangential direction thereof. The openings 5 may be formed by a punch press to provide a guide wall extending inwardly of the chamber 2.
The liquid introduced into the chamber 2 flows in a tangential direction to generate a vortical flow. As is well known, due to centrifugal force, the bubble-rich liquid is then concentrated in the center portion of the vortical flow and fine bubbles are combined together to form greater size bubbles. The liquid containing less bubbles concentrates in the vicinity of the peripheral wall of the chamber 2, where it is discharged through the holes 6 into the outer vessel 8 and then through the liquid discharge outlet 7. On the other hand, the bubble component concentrated at the center portion of the vortical flow enters into the center conduit pipe 9 and is discharged through the bubble discharge outlet 11.
It is to be noted here that bubble separation performance utilizing centrifugal force of the vortical flow is proportional to the square of the liquid flow velocity and inversely proportional to the radius of the chamber 2. Namely, at a position where the radius of the chamber is r, when a liquid having a density .rho.1 and bubbles having a density .rho.g flows at a flow velocity v and an angular velocity .omega., the liquid-bubble separation performance S can be expressed by the following equation: EQU S=(.rho.1-.rho.g).times..omega..sup.2 .times.r
Here, since .omega. can be expressed by v/r, the foregoing equation can be modified as: EQU S=(.rho.1-.rho.g).times.v.sup.2 /r
As seen from FIG. 1, since the vortical flow chamber 2 is constructed to have reduced radius (r) toward its lower portion, the bubble separation performance S becomes greater toward the lower portion.
The inventors herein have found that the shown type of the bubble separating apparatus is more effective for greater size bubbles. To enlarge the bubble size by combining a plurality of fine bubbles, a substantially strong vortex with laminar flow is required to be generated. The known apparatus is not considered sufficient from this viewpoint, because the annular pipe 3 communicating with the chamber 2 through a plurality of spaced openings 5, does not contribute to the generation of vortical flow. The liquid stream in the annular pipe 3 is a turbulent flow so that the fine bubbles contained in the liquid are not united together. Thus, the bubble separation is substantially solely achieved by the vortical flow in the chamber 2.